BAEL-2514 - Added unit test for Map processing

java-streams/src/test/java/com/baeldung/stream/StreamMapUnitTest.java

@@ -0,0 +1,65 @@
+package com.baeldung.stream;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+import static org.junit.Assert.assertEquals;
+
+public class StreamMapUnitTest {
+
+    private Map<String, String> books;
+
+    @Before
+    public void setup() {
+        books = new HashMap<>();
+        books.put("978-0201633610", "Design patterns : elements of reusable object-oriented software");
+        books.put("978-1617291999", "Java 8 in Action: Lambdas, Streams, and functional-style programming");
+        books.put("978-0134685991", "Effective Java");
+    }
+
+
+    @Test
+    public void whenOptionalVersionCalledForExistingTitle_thenReturnOptionalWithISBN() {
+        Optional<String> optionalIsbn = books.entrySet().stream()
+                .filter(e -> "Effective Java".equals(e.getValue()))
+                .map(Map.Entry::getKey).findFirst();
+
+        assertEquals("978-0134685991", optionalIsbn.get());
+    }
+
+    @Test
+    public void whenOptionalVersionCalledForNonExistingTitle_thenReturnEmptyOptionalForISBN() {
+        Optional<String> optionalIsbn = books.entrySet().stream()
+                .filter(e -> "Non Existent Title".equals(e.getValue()))
+                .map(Map.Entry::getKey).findFirst();
+
+        assertEquals(false, optionalIsbn.isPresent());
+    }
+
+    @Test
+    public void whenStringVersionCalledForExistingTitle_thenReturnISBN() {
+        String isbn = books.entrySet().stream()
+                .filter(e -> "Effective Java".equals(e.getValue()))
+                .map(Map.Entry::getKey)
+                .findFirst()
+                .orElse(null);
+
+        assertEquals("978-0134685991", isbn);
+    }
+
+    @Test
+    public void whenStringVersionCalledForNonExistingTitle_thenReturnNull() {
+        String isbn = books.entrySet().stream()
+                .filter(e -> "Non Existent Title".equals(e.getValue()))
+                .map(Map.Entry::getKey)
+                .findFirst()
+                .orElse(null);
+
+        assertEquals(null, isbn);
+    }
+
+}